Subsequent Event - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended			1 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2014 Subsequent Event Dividend Declared
Subsequent Event [Line Items]
Dividends declared	$ 0.36	$ 0.36	$ 0.36	$ 0.36	$ 0.31	$ 0.31	$ 0.31	$ 0.31	$ 1.44	$ 1.24	$ 0.92	$ 0.38
Dividend payable date												Mar. 07, 2014
Dividend payable, stockholders of record date												Feb. 20, 2014
Dividend announcement date												Jan. 31, 2014